In recent years, electronic appliances which require menu selections have been increasingly provided with touch panels which are pressed with a pen or a finger to make a desired menu selection in accordance with a screen display. Such electronic appliances employ various methods for identifying pressed positions on the panel.
Patent Document 1 discloses a touch panel with a built-in liquid crystal display device in which pressed positions are identified by obtaining potential differences between sensor lines and dummy lines, both of which are provided in the touch panel with a built-in liquid crystal display device. FIG. 14 provides (A) a plan view partially illustrating a display element portion of the conventional touch panel with a built-in liquid crystal display device disclosed in Patent Document 1, and (B) a cross-sectional view illustrating the display element portion in cross-section taken along line S-S shown in (A).
Referring to FIG. 14, the operation of the touch panel with a built-in liquid crystal display device for identifying a pressed position will be outlined. In the touch panel with a built-in liquid crystal display device, a TFT (thin-film transistor) substrate, which includes a glass substrate 500 on which display element portions 19 and a driver circuit (not shown) are formed, is disposed so as to be opposed to a CF (color filter) substrate, which includes a glass substrate 800 on which color filters, a common electrode, and so on, are formed. On the glass substrate 500, a plurality of data lines 540 made of a conductive film are formed so as to cross a plurality of gate lines 510 made of a conductive film different from that of the data lines 540. Furthermore, sets of sensor lines 550 and dummy lines 560 are formed, one set for each data line 540, so as to be parallel to the data lines 540 in the same layer, and sets of sensor lines 520 and dummy lines 530 are formed, one set for each gate line 510, so as to be parallel to the gate lines 510 in the same layer. Note that reference characters 610, 620, and 640 denote interlayer insulating films.
In such a touch panel with a built-in liquid crystal display device, when the surface of the CF substrate is pressed, the common electrode 840, which is formed on the surfaces of sensor spacers 830 provided on the glass substrate 800, makes contact with conductive pads 700 and 750, which are respectively connected to the sensor lines 520 and 550, so that a common voltage being provided to the common electrode 840 is provided to each of the sensor lines 520 and 550 via the conductive pads 700 and 750, respectively. On the other hand, the dummy lines 530 and 560 are provided with a reference voltage. Therefore, the touch panel with a built-in liquid crystal display device can compare the common voltage provided to the sensor lines 520 and 550 with the reference voltage provided to the dummy lines 530 and 560 to identify the pressed position on the CF substrate.